This invention relates to a delivery system for delivering molten metal to a molding cavity of a die-casting machine. Particularly, the delivery means or assembly features a gooseneck shaped molten metal delivery channel communicating to an injector and valve assembly within a housing, the latter immersed in a molten metal reservoir, and adapted to deliver, preferably a fixed charge, of molten metal directly to a mold cavity of a die-casting machine.
In conventional mold die-casting machines that die-cast miniature to medium sized parts, the molten metal delivery devices for conveying molten casting material to the mold cavity are generally shaped as a gooseneck. Such liquid molten delivery systems are particularly popular for delivering zinc from a reservoir furnace of molten metal to the die cavity where the casting operation takes place. Such gooseneck assemblies have typically relied on the co-operative arrangement of positioning the molten metal intake, and delivery port in relative co-operation with a piston to regulate the actual metal flowing through both ports, while the intake port communicates to the molten metal reservoir, and the delivery port directly to the mold or to a delivery channel communicating directly to the cavity of the mold. Such arrangements, particularly in non-corrosive metal applications such as molten zinc, have had the undesirable feature of allowing air to enter the molten metal intake conduit, particularly during the intake stroke of the piston; that is, the stroke which pulls metal from the molten reservoir into the delivery system. The air is thus entrained in the liquid metal in the delivery system. Prior art results of such air flows include bubbles impregnated within the finished casting or pitted cast surfaces. Further, wear on the molten metal flowing piston, which is the operative element for flowing the liquid metal, has been severe because the operative piston stroke was of necessity relatively long, thus increasing the tendency of wear on the piston; or, imposing constrictions on the fabrication of the piston and piston chamber, resulting in surfaces thereon being less than optimally smooth.
Prior art assemblies have attempted to overcome such deficiencies with improved gooseneck-type assemblies which incorporate therein a ball-valve structure similar to that described in Canadian Patent 802,100 issued 24 Dec., 1968 to Dynacast Limited. Modified goosenecks according to this structure lowered the amount of air admitted into the piston chamber; nevertheless, undesired drainage of molten metal from the piston chamber back into the molten metal reservoir occurred during the compression stroke of the piston. A major consequence of such structure in prior art systems was that drainage of molten metal occurred from the delivery piston chamber back into the molten liquid supply reservoir, but most importantly, this caused less than a "full charge" of molten metal being injected, from the delivery piston chamber into the mold cavity. Additionally, with heat and pressure losses, casting speeds and casting qualities have been substantially reduced from that which are theoretically possible. Prior art structures, though operative at a less than optimal speed and quality, fail as an accepted delivery system for corrosive molten metals such as aluminum, titanium and the like, since they corrode the operative components of the delivery system.